Salted Caramel-Chocolate Fudge Cake

Ingredients

• 1 cup boiling water
• 1 cup cocoa
• 3/4 cup butter
• 1 1/2 cups brown sugar
• 1/2 cup white sugar
• 2 eggs
• 1 teaspoon vanilla
• 1 3/4 cups all-purpose flour
• 1 1/4 teaspoons baking soda
• 1 1/4 cups buttermilk
• 1 cup chocolate chips
• 1/2 cup dark brown sugar
• 1/2 cup light brown sugar
• 2 tablespoons milk
• 1 tablespoon vanilla
• 2 cups butter
• 2 cups icing sugar
• 1/2 teaspoon course sea salt